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AEGs.G ENERGY MEASUREMENTS

EGG 10617-1230 UC-702 OCTOBER 1993

THE

REMOTE SENSING

LABORATORY . OPERATED FOR THE U.S. .

DEPARTMENT OF ENERGY BY EG&G/EM

AN AERIAL RADIOLOGICAL SURVEY OF THE VERMONT YANKEE NUCLEAR

o POWER STATION AND SURROUNDING AREA

VERNON, VERMONT DATE OF SURVEY: AUGUST 1989

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DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

This report has been reproduced directly from the best available copy.

Available to DOE and DOE contractors from the Office of Scientific and Technical Information, P.O. Box 62, Oak Ridge, Tennesse 37831; prices available from (615) 576-8401.

Available to the public from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22161.

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~Gc.G ENERGY MEASUREMENTS

EGG 10617-1230 OCTOBER 1993

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AN AERIAL RADIOLOGICAL SURVEY OF THE VERMONT YANKEE NUCLEAR

POWER STATION AND SURROUNDING AREA

VERNON, VERMONT

DATE OF SURVEY: AUGUST 1989

R. Reiman C. M. Bluitt

Project Scientists

REVIEWED BY

~A/~7--· H. W. Clark, Jr., Manager Nuclear Radiation Department

This Document is UNCLASSIFIED

C. K. Mitchell Classification Officer

This work was performed by EG&G/EM for the United States Nuclear Regulatory Commission through an EAO transfer of funds to Contract Number DE-AC08-88NV1 0617 with the United States Department of Energy.

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ABSTRACT

An aerial radiological survey was conducted over the Vermont Yankee Nuclear Power Station in Vernon, Vermont. during the period August 7 through August 17. 1989. The survey was conducted at an altitude of 300 feet (91 meters) over a 65-square-mile (168-square-kilometer) area centered on the power station. The purpose of the survey was to document the terrestrial gamma radiation environment of the Vermont Yankee Power Station and surrounding area.

The results of the aerial survey are reported as inferred gamma radiation exposure rates at 1 meter above ground level in the form of a contour map. Outside the plant boundary, exposure rates were found to vary between 6 and 10 microroentgens per hour (!J.R/h) and were attributed to naturally­occurring uranium, thorium, and radioactive potassium gamma emitters.

The aerial data were compared to ground-based "benchmark" exposure rate measurements and radionuclide assays of soil samples obtained within the survey boundary. The ground-based measurements were found to be in good agreement with those inferred from the aerial measuring system.

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CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Sections

1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2.0 Survey Site Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3.0 Natural Background Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

4.0 Survey Equipment and Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4.1 Aerial Measuring System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4.2 Ground-Based Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

4.3 Mobile Data Processing Laboratory................................................. 4

4.4 Survey Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.0 Data Reduction Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.1 Total Exposure Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.2 Man-Made Gross Count Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

6.0 Survey Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.1 Aerial Survey Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

6.2 Ground-Based Measurement Results............................................... 6

7.0 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figures

1 Aerial Photograph of the Vermont Yankee Nuclear Power Station and Surrounding Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 MBB B0-1 05 Helicopter with Detector Pods ........................................... . 3

3 Mobile Computer Processing Laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4 Terrestrial Gamma Exposure Rate Contour Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Typical Background Gamma Energy Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6 Net Gamma Energy Spectrum over Reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

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Tables

( 1 Exposure Rates from Aerial and Ground-Based Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 Radionuclide Assay of Soil Samples 9

c Appendix

A Survey Parameters .......................... . .... . ... . ... ..... ~ . . . . . . . . . . . . . . . . . . . . . . . . 1 0

References ll

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1.0 INTRODUCTION

An aerial radiological survey of the Vermont Yankee Nuclear Power Station and surrounding area in Vernon, Vermont, was conducted during the period August 7-17, 1989, at the request of the United States Nuclear Regulatory Commis­sion (NRC). The survey was performed using the Aerial Measuring System1 (AMS), operated by EG&G Energy Measurements, Inc. (EG&G I EM). for the United States Department of Energy (DOE). EG&G /EM routinely conducts aerial surveys for the DOE, the NRC, and other United States government agencies as part of an ongoing nationwide program to map and docu­ment the radiological conditions at various nuclear sites. Aerial radiological surveys have been effective in detecting regions of enhanced radiation, determining average ground-level exposure rates, and identifying specific radio­nuclides associated with regions of anomalous radiation levels.

The Vermont Yankee Nuclear Power Station is owned by the Vermont Yankee Nuclear Power Corporation. The power station contains a Gen­eral Electric boiling water reactor (BWR) capable of producing net electrical power of 1593 million watts. The unit was constructed in 1967 and be­gan serving the local communities in November 1972. The power station is situated on 127 acres on the east bank of the Connecticut River about 5 miles southeast of Brattleboro, Vermont, and 14.5 miles southwestofKeene, New Hampshire.

The present aerial survey was flown at an alti­tude of 300 feet (91 meters) using a pattern of nominally parallel flight lines spaced to cover the 65-square-mile (168-square-kilometer) area. The aerial data were used to derive expo­sure rates at 1 meter above ground level (AGL). In support of the aerial measurements, ground­based exposure rates and soil samples were obtained from various benchmark sites identi­fied by the aerial survey to contain only natural gamma activity. Radionuclide assay of the soil samples was performed to determine radio­isotopic concentrations. Oblique aerial photo­graphs of the Vermont Yankee Nuclear Power Station were also obtained in conjunction With the survey.

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2.0 SURVEY SITE DESCRIPTION

The Vermont Yankee Nuclear Power Station is located in Wildham County, about 5 miles (8 kilometers) southeast of the city of Brattleboro, Vermont. Presented in Figure 1 is a large-scale aerial photograph (June 1989) of the power sta­tion and surrounding area. The survey bound­ary, outlined in Figure 1, encompasses a 65-square-mile ( 168-square-kilometer) area centered on the power station. The Connecticut River, which defines the Vermont-New Hamp­shire state line, splits the survey area nearly in half. The New Hampshire side of the river con­sists of sparsely populated, rolling hills used primarily for farming. The Vermont side of the river is comprised mostly of wetlands and marshlands.

3.0 NATURAL BACKGROUND RADIATION

Natural background radiation originates from radioactive nuclides which are present in vari­ous low-level concentrations in the earth and

·atmosphere, as well as cosmic rays entering the earth's atmosphere from outer space. Terres­trial radiation, which originates primarily from the uranium decay chain, the thorium decay chain, and radioactive potassium, is detected at the surface of the earth at exposure rates between 1 and 15 !J.R/h (9 and 130 mrem/yr). The exposure rates from terrestrial radio­nuclides are dependent on the composition of soil and bedrock near the point of interest. In addition to the above-mentioned sources of nat­ural radiation, cesium-137 (137Cs), a product of nuclear fission, is present worldwide in trace quantities from fallout due to aboveground nuclear tests conducted until the early 1960s. Exposure rates due to I37Cs in the environment are typically less than 1 JA.R/h.2

Radon gas, a by-product in the decay chain of both uranium and thorium, diffuses through the soil into the atmosphere and contributes to the radiation levels near the surface of the earth. The radon concentration in a particular area, however, depends on several factors including meteorological conditions, mineral composi­tions, and permeability of the soil. Airborne radiation from radon and its decay products typically contributes from 1% to 10% to the nat­ural background radiation.

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0 4000 8000 FEET 1 1 - , , , ' r r •

0 I 1200 2400 METERS

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Soil sample sites are shown in colored numerals.

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FIGURE 1. AERIAL PHOTOGRAPH OF THE VERMONT YANKEE NUCLEAR POWER STATION AND SURROUNDING AREA

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Cosmic rays, high-energy radiation originating from outer space, also contribute to the levels of natural background radiation. The cosmic rays from outer space shower the earth with a nearly constant flux of radiation which interacts with elements in the earth's atmosphere and soil, producing an additional source of background activity. Radiation levels due to cosmic rays vary with altitude and geomagnetic latitude. Typical values range from 3.3 f.LR/h at sea level to 12 f,tR/h (27 to 100 mrem/yr) at elevations of 10,000 feet (3,000 meters).3 For the Vermont­New Hampshire area, the cosmic ray contribu­tion is about 3.7 f.LR/h.

4.0 SURVEY EQUIPMENT AND PROCEDURES

4.1 Aerial Measuring System

The low-altitude aerial survey was flown using a Messerschmitt-Bolkow-Blohm (MBB B0-105) helicopter (Figure 2). The twin-engine heli­copter was outfitted with two gamma detection pods and a Radiation and Environmental Data Acquisition and Recorder System (REDAR IV). The two large detector pods were mounted on the sides ofthe skid rack on the helicopter. Each pod housed four 4- x 4- x 16-inch log-type, thallium-activated sodium iodide, Nai(Tt'), gamma ray detectors. The energy response of the detector array was calibrated using the 60-keV and 1,274-keV gamma rays from americium-241 (241Am) and sodium-22 (22Na), respectively. At an altitude of 300 feet (91 meters), the AMS gives accurate terrestrial gamma exposure levels up to 70 f.LR/h. The dynamic range of the AMS is extended to 560 f.LR/h through the use of a single 4- x 4- x 16-inch detector. Appendix A presents a list of the survey parameters.

Data acquisition was performed using REDAR IV, a rack-mounted, portable, multimicro­processor real-time analysis system. The system was designed to operate in adverse conditions, such as those encountered in heli­copter or fiXed-wing platforms. The REDAR IV system recorded on magnetic tape data from the

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FIGURE 2. MBB 80-105 HELICOPTER WITH DETECTOR PODS

detector array, ambient temperature and baro­metric pressure sensors, radar altimeter, sys­tems live-time information, and the helicopter positioning system. Visual inspection of the data by on-board personnel was provided by a video display. The REDAR IV system was also equipped with the capability for real-time in­spection of gamma energy spectra.

Aircraft positioning was established using an ultrahigh-frequency ranging system (URS), an inertial navigation system (INS). and the radar altimeter. Two ground-based transponders were periodically interrogated by a master unit housed in the helicopter. Available URS trans­ponder locations were much less than ideal. As a consequence, the quality ofthe real-time posi­tioning and steering information was strongly degraded. Real-time flight direction was · done largely by visual and/or dead-reckoning tech­niques. However, flight paths could be recon­structed with reasonable accuracy (± 100 feet) from the post-flight analysis of the INS data. Therefore, radiation data could be contoured adequately.

4.2 Ground-Based Measurements

Total exposure rates and soil samples were obtained from four ground-based benchmark sites for comparison to the aerial measure­ments. The four sites, designated in Figure 1, were identified by the aerial survey as having only natural background radiation. At each site, total exposure rates were measured with a gam­ma ionization chamber and five soil samples were taken for laboratory analysis. Soil sample

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analysis was performed at the EG&G /EM Santa Barbara Laboratory in accordance with estab­lished procedures. 4

4.3 Mobile Data Processing Laboratory

The operations base for the survey was the Keene Airport in Keene, New Hampshire, located approximately 14 miles (22 kilometers) east of the Vermont Yankee Nuclear Power Sta­tion. The Radiation and Environmental Data Analyzer and Computer (REDAC) system, a mobile computer laboratory for analysis of the aerial survey data (Figure 3), was located at the operations base. The REDAC system consists of a Data General MV-7800XP computer with 4 megabytes of memory, a 1.1-gigabyte Winches­ter disk for mass storage, two 9-track tape drives for data transfer and archiving, a 36-inch-wide plotter for data contouring, a laser printer. and three video graphics display terminals .

FIGURE 3. MOBILE COMPUTER PROCESSING LABORATORY

The REDAC system utilizes an extensive soft­ware library for analysis of the pre- and post­flight REDAR IV and detector system checks and provides on-site preliminary analysis of the aerial measurements on a flight-by-flight basis.

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4;4 Survey Procedures

The aerial survey over the Vermont Yankee Nuclear Power Station and surrounding area was conducted according to standardized pro­cedures,l,5 which will be discussed only briefly in this section. First. the perimeter ofthe survey area was flown utilizing roads easily identifiable on the large-scale aerial photograph. Roadway intersections and landmarks were noted by flightcrew personnel for future use in scaling the radiation contour data to aerial photo­graphs.

Altitude profiles were then flown over desig­nated water and land test lines. An altitude pro­me consists of several flights over a test line at nominal altitudes ranging from 200 feet (61 meters) to 800 feet (244 meters). The water test line was flown approximately one-half mile from the banks of the Connecticut River, which is located about 10 miles (16 kilometers) north of the survey site. Data accumulated during the water test line profile were used to determine the nonterrestrial background radiation which originates from airborne radon, the helicopter and detector system, and cosmic rays. Typical­ly, the water test line was flown at the survey altitude at least once during each survey flight to monitor fluctuations in the radon concentra­tion. A section of open field designated by a fence line was chosen for the land test line. The terrestrial data from the land test line profile, corrected for the nonterrestrial background, were used to derive the air attenuation coeffi­cient.

The aerial survey covered an area of 65 square miles (168 square kilometers) as outlined in Fig­ure 1. Sixty flight lines were flown at an altitude of 300 feet (91 meters) AGL. All flights were flown at an average ground speed of 70 knots (36 meters/sec). The aerial survey over the Vermont Yankee Nuclear Power Station and surrounding area was completed in twelve flights over a period of ten days.

5.0 DATA REDUCTION PROCEDURES

5.1 Total Exposure Rate

A contour map of the total gamma radiation exposure rates in f!R/h at 1 meter AGL was pre­pared from the aerial data. The total exposure

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rate contour map was derived from the gross count rates and aircraft positioning coordinates recorded during the survey flights. The gross count rate data were determined from the inte­grated yield of all gamma activity within the en­ergy range 38 through 3,026 keV. Gross count rates in counts per second (cps) obtained from the aerial survey were converted to exposure rates in !J.R/h at 1 meter above ground level ac­cording to:

ER (p.Rjh) = GC-B e(A-300J.C ( 1) 692

where GC = gross count rate at survey altitude

(cps) B = background count rate at survey

altitude (cps) A = survey altitude (feet) c = air attenuation coefficient

An air attenuation coefficient having a value of 0.0019 was determined empirically from the background-subtracted gross count data ob­tained from the altitude profile over the land test line. The gross count rates were converted to ex­posure rates using a conversion factor of 692 cps/(!J.R/h) at 300 feet (91 meters) derived from data obtained at the Calvert County calibrationS range near Washington, D.C. The reported expo­sure rates include a contribution from cosmic rays, which is estimated to be 3. 7 !J.R/h for the Vernon, Vermont area.

The total gamma exposure rates measured using the AMS represent average exposure rates for gamma rays emitted from nuclides distrib­uted over a large area on the ground. The aver­aging process is a function of the angular response of the detector system and the motion of the aircraft during data accumulation. In gen­eral, two-thirds of the detected gamma rays emanate from a circular area having a radius which is nearly the same as the detector altitude above ground level.

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5.2 Man-Made Gross Count Rate

The aerial survey data were also used to deter­mine the location of man-made radionuclides. The man-made gross count (MMGC) is defined as the fraction of the gross counts which are directly attributed to gammas from man-made radionuclides. In general, evidence for the detection of man-made radioisotopes can be found from increases in the gross count rates. However, slight changes in the gross count rates are not considered adequate reason to suspect a man-made isotope. Slight variations in the gross count rates can be attributed to fluctua­tions in the geologic structure as well as changes in the ground coverage.

A more conclusive approach for detecting man­made isotopes involves a comparison of gross counts from various regions of the gamma ener­gy spectrum. In particular, the ratio of spectral intensities from different regions of the gamma spectrum will remain nearly constant when only background radiation is present. Although this procedure can be applied to any region of the gamma spectrum, the most common prac­tice is to place into the source window all counts below 1,394 keV, i.e., where most man-made radiation occurs, and to place into the back­ground window all counts above 1,394 keV. The MMGC algorithm has been found to be sensitive to low levels of man-made radiation (i.e., < 1 !J.R/h) even in the presence oflarge variations in the natural background.

The MMGC rate can be expressed analytically in terms of the integrated count rates in specific spectral energy windows (in keV) from the gam­ma energy spectrum

1394 keV

MMGC = I Counts£ E=3BkeV

where

1394 keV

I E=38keV

3026 keV

- K • I Counts£ E=/394 keV (2)

= integral count rate in the energy window from 38 to 1,394 keV

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I E=l394 keV

and

= integral count rate in the energy window from 1,394 to 3,026 keV

1394 keV

K= I I 3026keV

_ E=J~keV (3) E=38 keV

The constant, K, was obtained from the summa­tion spectrum composed of the gamma spectra acquired over a region of the survey area which was identified to contain only gamma activity from naturally-occurring radionuclides. The re­sultant MMGC will yield an average value equal to zero for areas containing only natural radio­nuclides and a value greater than zero for areas containing man-made radionuclides. Identifi­cation of the radionuclides responsible for anomalous behavior in the man-made gross count data can be obtained from the corre­sponding gamma energy spectra.

6.0 SURVEY RESULTS AND DISCUSSION

6.1 Aerial Survey Results

Presented in Figure 4 is a contour map showing the total gamma exposure rates (!J.R/hl at 1 me­ter AGL inferred from the aerial data at the Vermont Yankee Nuclear Power Station and surrounding area. The contour map is super­imposed on a large-scale aerial photograph. Exposure rates were found to vary from 6 to 1 0 !J.R/h outside the plant boundary; however, directly over the power plant, rates of approxi­mately 27 to 91. !J.R/h were discerned. Included in the exposure rate data is a cosmic ray con­tribution of 3. 7 !J.R/h. The location of the nuclear power plant is readily discernable from the series of concentric rings near the center of the map.

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The exposure rates measured outside the plant boundary are attributed to naturally-occurring radionuclides in the environment and are fairly uniform, varying from 6 to 10 !J.R/h. A typical gamma energy spectrum obtained outside the plant boundary is presented in Figure 5. The most prominent gamma peaks are identified as those from naturally-occurring radionuclides from the uranium and thorium decay chains as well as radioactive potassium-40 (40K).

A net gamma energy spectrum obtained over the plant is presented in Figure 6. Peaks observed were 1,173 and 1,332 keV associated with cobalt-60 ( 60Co), an activation product, and a 511-keV annihilation peak associated with nitrogen-16 ( 16N). Nitrogen-16 is produced by an (n,p) reaction with oxygen-16 (16Q) during reactor operations. The 16N decays via the emis­sion of 6.1 and 7.1 MeV gamma rays resulting in a high count rate in the high-energy portion of the spectrum and an annihilation gamma ray at 511 keV. These peaks are normal for BWR reactors like Vermont Yankee.

In addition to the exposure rate contours (Figure 4), a man-made gross count (MMGC) contour map was also produced. The only sig­nificant gamma activity shown by the MMGC extraction was directly over the plant. Because plant activity is adequately described by the ex­posure rate contour, the MMGC contour is not presented in this report.

6.2 Ground-Based Measurement Results

The locations of the four ground-based mea­surements are identified in Figure 1. Total expo­sure rates and soil samples were obtained at four benchmark sites for comparison and verifi­cation of the aerial measurements. 7 A compari­son of the exposure rates from the aerial and ground-based measurements is given in Table 1. Both soil analysis estimates and the inferred aerial results include an additional 3 .7 !J.R/h cosmic contribution for direct comparison with

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BLACK AND WHITE CONTOUR LINES ARE USED FOR CLARITY.

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• Calculated from aerial data obtained at an altitude of 91 meters (300 feet). Values include an estimated 3.7 tJR/h due to cosmic ray contributions.

FIGURE 4. TERRESTRIAL GAMMA EXPOSURE RATE CONTOUR MAP

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EXPOSURE RATE LETTER AT 1 METER LABEL (tJR/h) *

A < 5

B 5- 7

c 7- 9

D 9- 11

E 11 - 13

F 13-27

G 27 - 91

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0 0 w C\1

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GAMMA ENERGY (keY} 3000

FIGURE 5. TYPICAL BACKGROUND GAMMA ENERGY SPECTRUM

the gamma ionization chamber readings. The results from the aerial and ground-based mea­surements are shown to be in excellent agree­ment.

Presented in Table 2 are the results of the radio­nuclide assay of the soil samples from the four benchmark sites. Soil sample results represent those from averages of five closely spaced sam­ples obtained from each site. In addition to the naturally-occurring isotopes from the decay chains (uranium and thorium) and 40K, all sam­pling sites exhibited a presence of 137Cs. The I37Cs is present in the environment as a result of worldwide fallout from aboveground nuclear tests conducted until the early 1960s. The level of I37Cs activity measured at the benchmark

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...1 wu zw Zen <t:w :X:w (.).,....

CI: II ww a.::::E en­........ zw =:~;::: 0...1 (.)

FS = 700

0 ...... .,.... 0 .,.... C')

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0 GAMMA ENERGY (keY} 3000

FIGURE 6. NET GAMMA ENERGY SPECTRUM OVER REACTOR

sites is typical of that measured at several loca­tions within the continental United States. 2

7.0 SUMMARY

An aerial radiological survey of the Vermont Yankee Nuclear Power Station was conducted during the period August 7 through August 1 7, 1989. An area of 65 square miles ( 168 square ki­lometers) was surveyed at an altitude of 300 feet (91 meters) using a pattern consisting of nomi­nally parallel flight lines. The typical terrestrial gamma radiation exposure rate was found to vary from 6 to 10 J.LR/h. No significant radioac­tivity was detected outside the plant boundary by the aerial measuring system.

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Table 1. Exposure Rates from Aerial and Ground-Based Measurements a

Site Soil Analysis b lon Chamberc Aerial Survey

1 8.6 + 0.8 7.9 + 0.5 8.5 + 1.5

2 9.3 + 0.8 8.8 + 0.5 7.2 + 1.5

3 8.6 + 1.5 7.5 + 0.5 8.5 + 1.5

4 7.2 + 0.8 6.9 + 0.5 6.5 + 1.5

a Exposure rate (!lR/h at 1 meter AGL) b Calculations include cosmic ray contribution of 3. 7 1-1R/h and a moisture correction of the form 1 /(1 +m) c Reuter-Stokes Model Number RSS-111, Serial Number G003

Table 2. Radionuclide Assay of Soil Samples

238U 232Th 137Cs 40K

Site %Moisture (ppm) (ppm) (pCi/g) (pCi/g)

1 22 2.1 + 0.4 8 +1 0.35 + 0.15 12 +1

2 17 2.8 + 0.2 9 +1 0.21 + 0.02 11.7+0.4

3 17 2.6 + 0.7 7 +2 0.34 + 0.09 11 +2

4 13 2.0 + 0.6 3.7 + 0.2 0.24 + 0.09 8.7 + 0.5

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Site:

Location:

Survey Dates:

Survey Coverage:

Project Scientist:

Survey Aircraft:

Acquisition System:

Detector Array 1:

Detector Array 2:

Lines Surveyed:

Survey Altitude:

Navigation System:

APPENDIX A

SURVEY PARAMETERS

Vermont Yankee Nuclear Power Station

Vernon, Vermont

August 7-17, 1989

65 mi2 (168 km2)

R. Reiman/C. M. Bluitt

MBB B0-1 05 Helicopter

REDARN

Eight 4- X 4- X 16-in Nal(Tf) crystals

One 4- X 4- X 16-in Nal(Tf) crystal

60

300ft (91 m)

URS/INS

Average Ground Speed: 70 knots (36 m/ s)

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REFERENCES

1. Jobst, J.E. "The Aerial Measuring System Program." Nuclear Safety. March/April1979, 20:136-147.

2. Mohr. R.A. and L.A. Franks. Compilation of Cs-137 Concentrations at Selected Sites in the Continental United States, Report No. EGG-1183-2437, S-724-R. EG&G Energy Measurements. Inc .. Santa Barbara. California. 1982.

3. Klement. A.W .. et al. Estimate of Ionizing Radiation Doses in the United States 1960-2000, U.S. EPA Report ORP/CD72-l. Environmental Protection Agency. Washington, D.C .. 1972.

4. Mohr, R.A.. A. E. Fritzsche, and LA. Franks. Ground Suroey Procedures, Report No. EGG-1183-2339, S-635-R. EG&G Energy Measurements. Inc .. Santa Barbara. California. 1976.

5. Boyns. P.K. The Aerial Radiological Measuring System (ARMS): Systems, Procedures and Sensitivity. Report No. EGG-1183-1691. EG&G Energy Measurements. Inc .. Las Vegas, Nevada,1976.

6. Mohr. R.A. Ground Truth Measurements at the Calvert County, Maryland Test Line, Report No. EGG-10282-2066. EG&G Energy Measurements, Inc., Santa Barbara, California, 1985.

7. Mohr, R.A. Private Communication. EG&G Energy Measurements, Inc., Santa Barbara, California, December. 1989.

11

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DISTRIBUTION

NRC/HQ LBL

E. D. Weinstein (1) H. A. Wollenberg

NRC/REGION I EG&G/EM

D. J. Chawaga (7) C.M. Bluitt H.W. Clark J. F. Doyle E. L. Feimster

DOE/DP L.A. Franks P. P. Guss

J. E. Rudolph (3) T. J. Hendricks D. A. Jessup C.K. Mitchell R.A. Mohr

DOE/HQ G.R. Shipman

OSTI (25) W. J. Tipton P.H. Zavattaro

DOE/NV

C.A. Cox (1)

LIBRARIES

RSL M. R. Dockter (1) SBO S. C. Ronshaugen (2) TIC

AN AERIAL RADIOLOGICAL SURVEY OF THE VERMONT YANKEE NUCLEAR

POWER STATION AND SURROUNDING AREA

VERNON, VERMONT EGG 10617-1230

DATE OF SURVEY: AUGUST 1989 DATE OF REPORT: OCTOBER 1993

LVAO LVAO LVAO LVAO SBO WAMD LVAO SBO LVAO SBO WAMD LVAO LVAO

( 1)

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